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ORIGINAL PAPER
The influence of atmospheric circulation conditionson Betula and Alnus pollen concentrations in Wrocław,Poland
Hanna Ojrzynska . Daria Bilinska . Małgorzata Werner . Maciej Kryza .
Małgorzata Malkiewicz
Received: 12 July 2019 / Accepted: 4 February 2020 / Published online: 12 February 2020
� The Author(s) 2020
Abstract The influence of atmospheric circulation
conditions on pollen concentrations of two taxons
(Betula and Alnus) in Wroclaw, Poland, for the years
2005–2014 was analysed. Pollen concentration was
analysed separately for twenty circulation types that
were determined using objective classification. The
results indicate the atmospheric circulation conditions
favourable for both low and high pollen concentra-
tions over Central Europe. Pollen concentrations vary
significantly according to circulation types. The
highest pollen concentrations for both taxons are
typical for warm, sunny, and dry anticyclonic circu-
lation types with anticyclone in the lower and upper
troposphere, especially for types with advection from
the SW. The lowest pollen concentrations are
observed for cold, wet, and cloudy cyclonic types
with advection from the northern sectors. There is also
a positive and statistically significant trend in the
frequency of circulation types favourable for high
concentrations of Betula and Alnus.
Keywords Pollen � Circulation types � Betula �Alnus � Central Europe
1 Introduction
According to the epidemiology of allergic diseases, on
average 14.9% of Poles’ show weakly positive reac-
tions to birch pollen and almost 8.1% show allergy
symptoms. In the case of alder, these numbers shrink
to 11.1% and 4.6%, respectively (Samolinski et al.
2014). Pollen grains constitute an important issue
affecting human health because they induce allergenic
diseases like asthma, rhinitis, and allergic conjunc-
tivitis (Traidl-Hoffmann et al. 2003). The severity of
symptoms increases as concentration of aeroallergens
rises (Rapiejko et al. 2007). For the most part, the
thresholds depend on the taxon, whereas different
individuals may experience symptoms of varying
severity for the same concentration level (Veriankaite
et al. 2010). Relations between the clinical picture of
allergic diseases and the level of pollen count in
Poland have been studied by Rapiejko et al. (2007).
Their study has shown that the first symptoms of the
upper respiratory track in patients allergic to birch
were visible during exposure to concentrations of
20 pollen m-3 (25% of subjects were sensitized to
birch pollen). Symptoms were noted in all the subjects
sensitized to birch pollen at concentrations of approx-
imately 75 pollen m-3, and at concentrations of
H. Ojrzynska (&) � D. Bilinska � M. Werner � M. Kryza
Department of Climatology and Atmosphere Protection,
University of Wrocław, Kosiby 8, 51-621 Wrocław,
Poland
e-mail: hanna.ojrzynska@uwr.edu.pl
M. Malkiewicz
Laboratory of Paleobotany, Department of Stratigraphical
Geology, Institute of Geological Sciences, University of
Wrocław, Cybulskiego 30, 50-205 Wrocław, Poland
123
Aerobiologia (2020) 36:261–276
https://doi.org/10.1007/s10453-020-09629-9(0123456789().,-volV)( 0123456789().,-volV)
120 pollen m-3, the symptoms were intensified. For
the alder, these values were 45 pollen m-3 (first
symptoms), 85 pollen m-3 (symptoms in all sensi-
tized subjects), and 95 pollen m-3 (intensified symp-
toms), respectively.
Poland has been recognized as an area with large
amounts of birch and alder pollen (Skjøth et al. 2013).
According to Skjøth et al. (2008), the density of Betula
sp. in broad-leaved forests ranges from 5 to 40% in
lowland parts of the country and for Alnus sp. from 5 to
40% depending on the region.
The release of tree pollen is determined by several
factors that include the time of the day, biological and
meteorological parameters such as progress into the
pollen season, temperature, relative humidity, and
wind speed (Nowosad 2015). Both the initiation and
magnitude of the daily pollen release mostly depend
on daily temperatures. If certain thresholds are not
met, then flowering will not be initiated. Similar
dependencies are seen in many species, which means
that small changes in temperature (such as 2 �C) can
have quite an impact on the daily flowering (Dosio and
Paruolo 2011; Skjøth et al. 2015b). In general, during
the Betula pollen season the temperature is higher than
during the Alnus pollen season (Skjøth et al. 2015a).
Puc and Kasprzyk (2013) have found a negative
correlation between Alnus pollen concentration and
relative humidity for most of the investigated seasons.
Sofiev et al. (2013) have indicated a lower and upper
limit of relative humidity for birch emissions at 50%
and 80%, respectively. They have also reported that
even with a low wind speed but with a thermal
convection being developed, turbulence is sufficient to
release pollen from catkins. Strong wind stimulates the
release of pollen but only to a certain threshold value.
If the wind speed exceeds 5 m s-1, it no longer
influences the rate of pollen release because it is
limited by the amount of pollen grains in catkins
prepared to release (Sofiev et al. 2013). Menut et al.
(2014) found that temperature, precipitation rate, and
specific humidity are significantly correlated with the
measured pollen concentrations. Correlations between
meteorological factors and pollen concentrations in
Poland have been investigated (e.g. Weryszko-Ch-
mielewska et al. 2006; Myszkowska and Piotrowicz
2009; Grewling et al. 2012; Malkiewicz et al. 2014;
Nowosad et al. 2015; Puc et al. 2015). They also found
that meteorological factors have an enormous influ-
ence on pollen concentration.
A connection between pollen concentrations and
atmospheric fronts has been reported by Goyette-
Pernot et al. (2003) and Nowosad et al. (2015).
Nowosad et al. (2015) have shown a strong correlation
between temporal variations in Alnus, Betula, and
Corylus pollen counts in Poland on the one hand and
air mass exchange on the other. They suggested that
between 30 and 40% of variability in pollen counts is
related to the passage of a single weather front.
Goyette-Pernot et al. (2003) have reported that
passage of fronts often increases the occurrence of
regional scale ragweed pollen peaks in the city of
Montreal. They have also shown that anticyclonic
conditions are favourable for local pollen production
but inhibit dilution on larger scales. Grundstrom et al.
(2017) have found the approach based on weather
types to be a relatively simple method for character-
izing the weather condition in a synoptic scale, thereby
grouping together many meteorological variables that
are important for processes that determine the high or
low levels of pollen concentration. Conducted in
Gothenburg and Malmo, their study indicated that
high birch pollen concentrations are correlated with
dry and moderately calm conditions during an anticy-
clone and weather types with NE, SE, and S
geostrophic wind direction, whereas the lowest con-
centration levels were found in wet and windy types
with direction from SW, W, and NW and for the
cyclonic type (Grundstrom et al. 2017). The number of
studies that applied weather types for pollen analysis is
rather limited, and according to the authors, it has yet
to be done for Central Europe.
Long-range transport is another important factor
responsible for atmospheric pollen concentrations.
The transport of pollen from the south of Europe is
especially visible in periods before the local pollen
season starts in Central and Northern Europe (Ranta
et al. 2006; Skjøth et al. 2007). Source regions of
various pollens have been determined with the use of
back trajectory from the HYSPLIT model (Makra
et al. 2010; Hernandez-Ceballos et al. 2014; de Weger
et al. 2016; Bilinska et al. 2017). However, examples
from Poland show that long-range transport plays a
significant role in the concentrations of pollen that are
rare in the Polish environment, especially Ambrosia
(Stach et al. 2007; Smith et al. 2008; Kasprzyk et al.
2011; Bilinska et al. 2017). Concentrations of species
native to Poland are mainly influenced by local
sources but appear to be augmented by remote sources,
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262 Aerobiologia (2020) 36:261–276
particularly for Betula (Bogawski et al. 2019), though
only to a small degree for Alnus (Skjøth et al. 2015a).
The purpose of this study is to analyse how the
atmospheric circulation affects pollen concentrations
of Betula and Alnus in Wrocław, southwest Poland,
with the use of automatic classification of air circu-
lation types. The circulation conditions favourable for
low and high pollen concentrations were determined,
after which the circulation types that might lead to the
risk of pollen concentrations exceeding the threshold
values were identified. The main tested hypothesis is
the following: a high concentration of birch and alder
pollen occurs during the same circulation types with
upper anticyclonic vorticity and high temperature,
sunshine, and vapour pressure deficit.
Furthermore, the long-term trend in the frequency
of types favourable to high pollen concentrations is
analysed so as to ascertain whether the observed
climate changes increase the risk of above-threshold
episodes for Betula and Alnus.
2 Materials and methods
2.1 Study area
Wrocław is located on the bank of the Odra River in
the Lower Silesia region in the southwestern part of
Poland. The climate of Wrocław is temperate with
transition due to the influence of maritime and
continental air masses. The climatic conditions are
formed mainly by the Icelandic Low and Azores High
and seasonal by the Asiatic High and South-Asiatic
Low. The mean annual temperature reaches 8.7 �C(1971–2000) with minimum in January (- 0.9 �C)
and maximum in July (18.1 �C). The annual precip-
itation sum is almost 570 mm on 157 days with
precipitation. The highest monthly sum of precipita-
tion is observed in July (90.8 mm) and the lowest in
February (24.1 mm). The growing season lasts
228 days (Głowicki et al. 2005).
According to the lexicon of the greenery of
Wrocław (Binkowska et al. 2013), the dominant
species in the city of the Betula type is Betula
pendula, but also present are individual specimens of
Betula papyrifera, Betula pubescens, and Betula utilis.
Under this reference, the dominant species for
Wrocław’s Alnus type is Alnus glutinosa.
2.2 Pollen data
The daily airborne alder and birch pollen concentra-
tion data represent the 10-year period from 2005 to
2014. We calculated the pollen concentration based on
pollens gathered at the Wrocław station (51.1164N,
17.0278E) with a Burkard 7-day volumetric pollen
trap. The sampler is located on the roof of the building
at a height of 20 m above ground level near the centre
of the city. The sampling site is surrounded by a dense
urban build-up area and small patches of greenery. To
the north of the building grow small birches and
several horse-chestnut trees and to the south of the
building is an alley of plane trees (Malkiewicz et al.
2014).
Pollen grains were counted under a light micro-
scope with 400 magnification along four longitudinal
transects. The results were expressed as the number of
pollen grains per cubic metre of air, i.e. as a daily mean
value (pollen m-3) (Malkiewicz et al. 2014). Airborne
pollen is counted following the recommendations of
the International Association for Aerobiology (Galan
et al. 2014). The seasonal pollen’s characteristics were
counted using the 95% method.
The number of days with pollen concentration
exceeding the threshold values for the occurrence of
allergic reactions was counted for each circulation
type. We used the threshold values of 85 pollen m-3
for Alnus and 75 pollen m-3 for Betula (Rapiejko
et al. 2007; Bergmann et al. 2008), which indicate that
allergy symptoms have been noted in all sensitized
subjects.
2.3 Meteorological data
The daily data of meteorological elements were taken
from Wrocław Strachowice Airport’s measuring sta-
tion (51.1N, 16.883E) of the Institute of Meteorology
and Water Management—National Research Institute.
Data comprising air temperature, sunshine duration,
amount of precipitation, vapour pressure, relative
humidity, fog duration, wind speed, and pressure were
used. The vapour pressure deficit was calculated with
the use of vapour pressure and relative humidity data
following Teten’s formula (Campbell and Norman
1998). The meteorological data were used to present
the average meteorological conditions during each
circulation type. Additionally, the meteorological
factors described below were prepared for the sake
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Aerobiologia (2020) 36:261–276 263
of ascertaining if there is a difference between pollen
concentrations in specific circulation types when the
values of meteorological elements are higher or lower
than their appropriate means. The use of meteorolog-
ical factors was connected with the assumption of a
multifactor ANOVA.
The mean values of the analysed meteorological
elements were calculated for each of the twenty
defined circulation types. Based on those means, the
meteorological factors for each day and elements were
calculated. The factors received a value of 1 when the
daily value of a particular meteorological element was
greater than the adequate meteorological mean, and 0
if it was less than the mean. The meaning of the factors
of temperature is as follows: 1—‘‘warm’’, 0—‘‘cold’’;
for sunshine duration 1—‘‘sunny’’, 0—‘‘cloudy’’; for
vapour pressure deficit 1—‘‘dry’’, 0—‘‘wet’’; for
relative humidity 1—‘‘wet’’, 0—‘‘dry’’; for wind
factor 1—‘‘windy’’, 0—‘‘calmly’’; and for pressure
1—‘‘high’’, 0—‘‘low’’. Only the fog and precipitation
factors were specified as 1 when the phenomenon
occurred and 0 when it did not.
2.4 Circulation types
Air circulation types were determined for each day of
the pollen seasons (February–May) for the years
1948–2017 according to a simplified methodology of
automatic classification developed for the Lower
Silesia region (Ojrzynska 2015; Ojrzynska et al.
2017). Twenty types of circulation were analysed.
The name of each circulation type is built according to
the scheme: AABB, where AA corresponds to the
direction of advection (SW—southwest, NW—north-
west, SE—southeast, NE—northeast, XX—indeter-
minate direction). BB describes the type of lower and
upper vorticity (CC—lower and upper cyclonic, CA—
lower cyclonic, upper anticyclonic, AA—lower and
upper anticyclonic, AC—lower anticyclonic, upper
cyclonic). In this study, we have not used the
classification of ‘‘wet’’ and ‘‘dry’’ circulation types
because the main classification factor—precip-
itable water—describes the water content in a whole
column of troposphere. This information cannot be
directly converted to vapour pressure near the surface
and therefore cannot be linked directly with pollen
emission.
All criteria of circulation types’ classification were
determined with the use of gridded meteorological
data (2.5� 9 2.5� spatial resolution, 24-h temporal
resolution) from NCEP/NCAR reanalysis (Kalnay
et al. 1996). The data were interpolated with the use of
spline function in the area of southwestern Poland to a
spatial resolution of 5 km 9 5 km. Classification of
circulation types was done for each grid cell sepa-
rately. To determine the circulation type for each
individual day, the prevailing type was calculated by
applying the mode function for all the 5 km 9 5 km
grid cells. This was done separately for the direction of
advection and vorticity. Direction of advection is
classified on the basis of wind direction from the
700 hPa isobaric level, if wind speed exceeds 2 m s-1.
In situations with a wind speed of lower than 2 m s-1
or when no prevailing wind direction is determined,
the XX type is noted. Types of vorticity are calculated
based on geopotential values from the 850 hPa (lower
vorticity) and 500 hPa (upper vorticity) isobaric levels
by means of the formula r2/, where r is the nabla
operator and / is the geopotential value. A positive
value of r2/ is classified for the cyclonic type, and a
negative one for the anticyclonic type.
2.5 Statistical analysis
The analysis has three steps. First, we look for the
relations between pollen concentrations and circula-
tion types with frequency above 4% in the analysed
pollen seasons. Second, we focus on relations between
the pollen concentrations and specific meteorological
elements, as measured at weather station in Wrocław.
Finally, we look for possible combinations of these
effects using the multi-factor analysis of variance.
The relations between circulation types, meteoro-
logical elements, and pollen concentrations during the
pollen seasons were analysed separately for each
taxon with the use of R software for statistical
computing (R Core Team 2014) with packages: cor,
nortest, tidyverse, and corrplot. For the pollen seasons
of each taxon, the circulation types with the highest
means of pollen concentration were selected. The
number of days with pollen concentration exceeding
the threshold values for the occurrence of allergic
reactions (Alnus C 85 pollen m-3, Betula C 75 pol-
len m-3; Rapiejko et al. 2007; Bergmann et al. 2008)
was counted for each circulation type.
To check whether there is any influence of circu-
lation types on pollen concentration, the correlation
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264 Aerobiologia (2020) 36:261–276
between the seasonal pollen integral (SPIn) in the
years that followed and the frequencies of particular
circulation types was calculated with the use of the
Pearson coefficient of determination (confidence
level = 0.95). Correlation analysis was also carried
out to quantify the relation between pollen concentra-
tion and meteorological elements on the one hand and
pollen seasonal length in the entire analysed period on
the other.
Because of the qualitative characteristic of circu-
lation types’ data, the diversity of pollen concentra-
tions in circulation types was analysed with the use of
an analysis of variance (ANOVA). To determine
whether meteorological conditions influence pollen
concentration independently or jointly with circula-
tion types, the multifactor ANOVA was used. The
assumption of normality of pollen data was almost
fulfilled after applying log transformation. According
to Glass et al. (1972) and Lix et al. (1996), ANOVA is
not very sensitive to moderate deviations from
normality. The homogeneity of data variance was
checked with the use of Levene’s test.
The analysis of the circulation types’ frequency
trends has been done for the last 70 years (1948–2017)
to ascertain whether there is any tendency of occur-
rence among the circulation types favourable to high
pollen concentration. The Mann–Kendall test for
monotonic trend was carried out, and Sen’s slope
estimator was calculated with the use of R software for
statistical computing. The analysis concerned poten-
tially the entire pollen season and the particular
months for Alnus (February–April) and Betula (April–
May).
3 Results
3.1 Characteristic of circulation types
during the pollen seasons
For SW Poland and Wrocław, the pollen season covers
mainly February–April for Alnus and April–May for
Betula (Tables 1, 2). For the years being analysed, no
overlap between pollen seasons for Alnus and Betula
was observed. The average seasonal pollen integral
reaches 3562 pollen m-3 for Alnus, whereas
8570 pollen m-3 for Betula with the average length
of the pollen season equalling 31 and 22 days,
respectively. Alnus has a more diverse pollen seasonal
length (standard deviation reached almost 13 days for
Alnus and 5 days for Betula), whereas Betula has a
more differentiated SPIn than Alnus. For both taxons,
the daily maximum concentration in the analysed
seasons reached almost 30% of the average SPIn.
There is no statistically significant correlation
between the length of the pollen season and SPIn for
both Alnus and Betula. Significant correlations are
noted for both analysed taxons in terms of SPIn and
frequency of specified circulation types. A negative
correlation concerns the Alnus pollen season between
SPIn and the frequency of lower and upper cyclonic
type NWCC (- 0.73). For Betula, a positive correla-
tion between SPIn and the frequency of types with
lower anticyclone is observed: NEAC (0.70) and
SWAC (0.70; Table 3).
The frequencies of circulation types during the
analysed pollen seasons are summarized in Fig. 1. The
lower and upper anticyclonic types with advection
from NE, NW, and SW are dominant. For the Alnus
pollen seasons, a relatively high frequency is observed
for lower and upper cyclonic types from SW. For the
Betula pollen seasons, there is increased frequency of
NE types. Other circulation types occur less often than
7% (17 days for Alnus and 14 for Betula in 10 pollen
seasons; usually 1–2 days for each pollen season).
Regardless of the specific circulation types, the
contribution of days with high pollen concentration
(Alnus C 85 pollen m-3, Betula C 75 pollen m-3)
to the whole number of days in the analysed period
is higher for Betula than for Alnus. A high contribution
of days with high Betula pollen concentrations is
observed in the most frequent anticyclonic types
(NEAA, NWAA, SWAA) and in types with advection
from the SW (SWCC, SWCA, SWAC). For Alnus, the
contribution of days with high pollen concentration
exceeding the value of 50% is observed only for the
SWAA type.
The specific circulation types represent different
combinations of meteorological conditions (Fig. 2).
For the Alnus pollen season, the highest average
temperatures and the longest sunshine duration with
high vapour pressure deficit and low amount of
precipitation as well as low wind speed are noted for
the lower and upper anticyclonic types SEAA, SWAA,
and partly for NEAA. Similar conditions for Betula are
observed partly for the type SWAA. The coldest and
cloudiest types with a low average vapour pressure
deficit and average precipitation above 1.2 mm as well
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Aerobiologia (2020) 36:261–276 265
as the highest wind speed are types SWCC and SWCA
for both taxons and additionally NWCC for Alnus.
Regardless of the taxon, types with lower anticyclone
and upper cyclone are mostly colder and drier than
types with lower cyclone and upper anticyclone even
though the average sunshine duration in the former
group is more often higher.
3.2 Pollen concentration in particular circulation
types
The Alnus pollen concentration according to the
circulation types is presented in Fig. 3. The highest
median value of pollen concentration (nearly 200 pol-
len m-3) is observed for SWAA. For SWAA, the
pollen concentration exceeds 300 pollen m-3 in 25%
of days and in some cases reaches almost 1000 pol-
len m-3. Very high concentrations are also noted for
the lower and upper anticyclonic types with advection
from NE and a maximum value 1034 pollen m-3 as
well as for SWCC, SWCA, and NWAC; however,
these are rare and do not influence the median
significantly. High Alnus pollen concentrations,
exceeding the threshold value of 85 pollen m-3, are
observed for all circulation types except for the lower
and upper cyclonic NWCC. The variability in mean
concentration of Alnus in specific circulation types is
high within a range of nearly 0 pollen m-3 for NWCC
to ca. 200 pollen m-3 for SWAA (Fig. 4). For most
types, the mean concentration varies from 50 to
130 pollen m-3.
Table 1 Basic characteristics of Alnus pollen seasons
Year Day of season start Length of the season Seasonal pollen integral (SPIn) Maximum pollen concentration
2005 17.03 19 5024 1034
2006 27.03 14 3737 881
2007 03.02 52 1019 189
2008 25.01 38 5731 484
2009 03.03 34 1234 204
2010 17.03 13 3750 987
2011 26.02 33 3124 730
2012 1.03 28 2902 532
2013 05.03 48 4695 881
2014 10.02 33 4402 785
Table 2 Basic characteristics of Betula pollen seasons
Year Day of season start Length of the season Seasonal pollen integral (SPIn) Maximum pollen concentration
2005 12.04 19 4849 1626
2006 19.04 21 15,373 2368
2007 07.04 20 4445 1322
2008 09.04 27 9751 1452
2009 07.04 20 3802 1317
2010 09.04 22 9348 1779
2011 05.04 25 4481 843
2012 04.04 28 14,924 1807
2013 19.04 12 5584 1378
2014 30.03 27 13,141 2247
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266 Aerobiologia (2020) 36:261–276
The highest mean and median values of Betula
pollen concentration are observed in similar types for
Alnus as well (Figs. 3, 4, 5, 6). In circulation type
SWAA, the median values exceed 500 pollen m-3.
The highest single concentrations exceeding
1500 pollen m-3 are noted mainly for types with
lower and upper anticyclone (NEAA, NWAA,
SWAA) and lower cyclone, upper anticyclone (SECA,
SWCA—with maximum 2368 pollen m-3). For all
circulation types, the median values of Betula pollen
concentration exceed the allergic symptoms threshold
value. The mean pollen concentration for most types
reaches from 200 to 450 pollen m-3 (Fig. 6). The
lowest mean (under 100 pollen m-3) concerns the
NWAC circulation type.
The variability of both Alnus and Betula mean
pollen concentrations in days with specified conditions
described by meteorological daily factors of temper-
ature, sunshine duration, fog, precipitation, vapour
pressure deficit, relative humidity, wind, and pressure
is analysed and presented in Figs. 4 and 6. The highest
differences in the mean pollen concentrations concern
days with various temperature and vapour pressure
deficit factors. Noticeable effects are observed for the
sunshine duration factor, the relative humidity factor,
and for the Betula atmospheric pressure factor as well.
The differences in mean pollen concentrations
between ‘‘cold’’ and ‘‘warm’’ days and ‘‘wet’’ and
‘‘dry’’ days reach almost 90 pollen m-3 for Alnus and
200 pollen m-3 for Betula, whereas in particular
circulation types the differences are even higher
(Fig. 7). The correlations between pollen concentra-
tion and temperature, and between pollen concentra-
tion and vapour pressure deficit are positive for both
taxons, except that those for Alnus are slightly higher
than for Betula (Fig. 8). For Betula low positive
correlation was also noted between pollen concentra-
tion and sunshine duration, whereas there was also a
Table 3 Pearson’s
correlation coefficients for
SPIn and frequency of
particular circulation types
Significant correlations
(a\ 0.05) are shown in
bold
Alnus Betula
NEAA 0.04 - 0.48
NEAC 0.70
NECA - 0.3
NECC 0.01
NWAA - 0.19 - 0.22
NWAC - 0.1 - 0.44
NWCC - 0.73
SEAA - 0.38 0.06
SECA 0.45
SECC 0.33
SWAA 0.29 0.65
SWAC 0.18 0.70
SWCA 0.07 0.18
SWCC - 0.17 0.63
Fig. 1 Frequency of circulation types for Alnus (left side) and
Betula (right side) pollen seasons and contribution of days with
high pollen concentrations (Alnus C 85 pollen m-3,
Betula C 75 pollen m-3). Frequency is calculated from 10
analysed pollen seasons. Circulation types with frequency
below 4% were omitted
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Aerobiologia (2020) 36:261–276 267
negative correlation between pollen concentration and
precipitation and between pollen concentration and
atmospheric pressure.
The results of ANOVA largely support the findings
described above. The differences between pollen
concentrations are considerable in particular circula-
tion types; however, the same circulation types may
vary depending on temperature and sunshine duration,
just as in days with specific temperature factor or
sunshine duration factor for both Alnus and Betula
(Table 4). Additionally, for Betula the precipitation
factor is also a significant contributor. A combination
of several factors is also important for pollen concen-
trations. For both taxons, this includes various
Fig. 2 Meteorological
conditions of circulation
types for Alnus (a, b) and
Betula (c, d): average values
of sunshine duration,
temperature, vapour
pressure deficit (d), amount
of precipitation (R),
pressure, wind speed, and
relative humidity (f) in
specific circulation types.
Threshold values of vapour
pressure deficit, amount of
precipitation, and relative
humidity are the mean
values from all days in 10
pollen seasons
Fig. 3 Alnus pollen concentration (pollen m-3) in circulation
types with frequency [ 4% in the analysed pollen seasons;
boxplots width is proportional to the frequency of circulation
types; hinges show the first and third quartiles, the whiskers are
1.5 times the spread of hinges or data extreme (if 1.5 * the hinge
spread is smaller than the extreme value), and circles are the
outliers, which are above/below 1.5 times the box length
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268 Aerobiologia (2020) 36:261–276
circulation types with the sunshine duration factor, and
for Alnus also various circulation types with the
temperature factor (Table 4).
3.3 Trend analysis of circulation types’ frequency
For the last 70 years (1948–2017), weak but statisti-
cally significant trends of selected circulation types’
occurrence have been noted for circulation types
specific for high pollen concentrations. For the Alnus
pollen season (February–April) and Betula pollen
season (April–May), the frequency of groups of lower
and upper anticyclone types (AA) increases by 1 day
per 10 years (Fig. 9). A statistically significant posi-
tive trend is calculated for the NWAA type in March,
i.e. in the middle of a potential Alnus pollen season.
The same is for NWAA and SWAA in May, which is
important for Betula (Fig. 10). In May, a significant
decrease concerns the SWCC circulation type
(Fig. 10), whereas throughout the whole Betula pollen
season a negative trend is noted in the SECA type. No
circulation type shows any statistically significant
trend for February and April.
Fig. 4 Mean concentration of Alnus (pollen m-3) in particular circulation types and days with various meteorological factors. Bold
horizontal lines represent the mean concentration of Alnus for all analysed pollen seasons
Fig. 5 Betula pollen concentration (pollen m-3) in circulation
types with frequency[ 4%; boxplots’ width is proportional to
the circulation types’ frequency; the boxplot hinges show the
first and third quartiles, the whiskers are 1.5 times the spread of
hinges or data extreme (if 1.5 * the hinge spread is smaller than
the extreme value), and circles are the outliers, which are
above/below 1.5 times the box length
123
Aerobiologia (2020) 36:261–276 269
4 Discussion
In this paper, we have described the relations between
Alnus and Betula pollen concentrations on the one
hand and atmospheric circulation types on the other,
based on data from 10 pollen seasons gathered at
Wroclaw, SW Poland. The atmospheric circulation
types specified from information about the direction of
air masses’ advection as well as lower and upper
vorticity are characterized by different meteorological
elements. This complex description of weather con-
ditions made it possible to analyse the influence of
meteorology on pollen concentration and determine
the circulation types with the highest and lowest pollen
concentration. This approach was used earlier by
Grundstrom et al. (2017) for birch in Gothenburg and
Malmo. Our results show that, similar to the Swedish
study, the highest pollen concentrations for Betula and
Alnus are noted for warm, sunny, and dry anticyclonic
circulation types, especially when the anticyclone
vorticity concerns the lower and upper troposphere.
Regardless of the pollen taxon, the most favourable
conditions for high pollen concentration are observed
for type SWAA. The important role of the upper
anticyclone in raising the level of pollen concentra-
tions in the aforementioned circulation types is
connected with the descent of air masses. These
conditions inhibit the dilution of pollen on larger
scales (Goyette-Pernot et al. 2003).
The lowest pollen concentration concerns cold,
wet, and cloudy cyclonic types: SWCC, NWCC, and
NWAC. Contrary to Grundstrom et al. (2017) in terms
of birch in Sweden, the pollen concentrations of
Betula and Alnus in Wrocław are to a small extent
influenced by wind speed. However, this is difficult to
surmise, as the frequency of circulation types with
calm wind conditions (especially from XX group of
circulation types) favourable to pollen accumulation is
very low (below the threshold frequency of 4% in
pollen seasons). High pollen concentrations of both
analysed taxons are observed regardless of the direc-
tion of air masses’ advection. It confirms the role of
local pollen sources, as described by Skjøth et al.
(2015a).
The results of a multifactor analysis of ANOVA
confirm the influence of the air temperature and
sunshine duration on pollen release and atmospheric
concentration pollination. Faegri and Iversen (1989)
as well as Pacini and Hesse (2004) have underlined
vapour pressure deficit as the most important meteo-
rological element in the formation of pollen concen-
tration; however, temperature and sunshine duration
have a strong correlation with it. In this work, a
significant differentiation in pollen concentrations
between specified circulation types with various
meteorological conditions has been corroborated.
Additionally, it is also shown that the influence of
sunshine duration on both taxons has diversified the
Fig. 6 The mean concentration of Betula (pollen m-3) in particular circulation types and days with various meteorological factors.
Bold horizontal lines represent the mean concentration of Betula in the entire ten pollen seasons
123
270 Aerobiologia (2020) 36:261–276
pollen concentration in days with specific circulation
types. Regardless of taxon being analysed, in sunny
days pollen concentrations are higher than in cloudy
days in most of the circulation types. For Alnus and
Betula, the enormous difference in pollen concentra-
tion is connected especially with type SWCA and for
Betula also SEAA and SWAC.
Significant correlations between SPIn and the
frequency of selected circulation types show that
current meteorological conditions during the pollen
season affect not only the daily pollen concentration
but also the overall SPIn. The aforementioned corre-
lation is negative and pertains to the cold, wet, and
cloudy type NWCC for Alnus, whereas for Betula it is
positive and connected with warmer and more dry
types with lower anticyclone (NEAC and SWAC).
The correlation for birch is visible despite its biennial
cycle in SPIn (Grewling et al. 2012; Kubik-Komar
et al. 2019; Tseng et al. 2020). Factors recorded during
buds’ formation (especially a year before flowering)
are mentioned as the most important in SPIn mod-
elling (Dahl and Strandhede 1996; Grewling et al.
2012; Ritenberga et al. 2018). The results of this work
allow for the view that including the expected
frequency of circulation types may improve the
modelling of pollen season’s intensity.
The results of trend analysis for the frequency of
circulation types correspond to earlier conclusions
about changes in the air circulation frequency for East
and Central Europe presented by Bartoszek (2017) for
Fig. 7 The mean concentration of Alnus and Betula (pollen m-3) in circulation types and days with various temperature factors and
vapour pressure deficit factors
123
Aerobiologia (2020) 36:261–276 271
Fig. 8 The correlation table between pollen concentration and meteorological factors for Alnus and Betula; significance level—0.05,
X—statistically insignificant
Table 4 The results of
multifactor analysis of
variance ANOVA—the
factors with significant
pollen concentration of
Alnus and Betula
Significance codes: 0 ‘***’
0.001 ‘**’ 0.01 ‘*’ 0.05
Taxon Factors Significance
Alnus Circulation type ***
Temperature factor ***
Sunshine duration factor ***
Circulation type ? sunshine duration factor *
Circulation type ? temperature factor *
Betula Circulation type ***
Temperature factor **
Sunshine duration factor *
Precipitation factor *
Circulation type ? sunshine duration factor **
Fig. 9 Number of days for lower and upper anticyclonic (AA) types during the pollen season for Betula (April–May) and Alnus
(February–April) for the period 1948–2017. Trend line is in red
123
272 Aerobiologia (2020) 36:261–276
the period of 1871–2010. A direct comparison is
impossible because of differences in the applied
circulation types’ classifications; however, Bartoszek
(2017) has also shown an increasing tendency towards
anticyclonic types’ occurrence, which is indicated in
this work as favourable to high Alnus and Betula
concentrations. Still, studies by Hanewinkel et al.
(2012) or Dyderski et al. (2017) have come to the
conclusion of a decrease in the distribution range of
birch. A suitable habitat area in Poland is dwindling
due to climate change, which could limit pollen
concentration. This situation is not so clear for Alnus
(Sakalli 2017) but indisputably affects the results of
our study. The observed increasing frequency of
circulation types favouring a high pollen concentra-
tion concerns the last 70 years and is relatively weak
(1 day in every 10 years). The analysed pollen seasons
concern only the last 10-year period that is why there is
no clear trend towards SPIn increase, as could be
expected due to the increasing frequency of circulation
types favouring high pollen concentrations.
The findings of this work support some of the
earlier results from studies undertaken with different
methods, e.g. analysis of backward trajectories. The
analysis of circulation types brings some more insights
to the understanding of pollen concentration in Central
Europe. The method could be further applied to
pollen—climate changes-related studies, e.g. future
changes in the frequency of circulation types while
taking into account the changing pollen distribution
range. Recent findings presented by Rohrer et al.
(2017) for the Alpine region have shown that the
frequency of circulation types favourable to westerly
flows and connected with higher temperature and
humidity will increase in the spring until the end of the
twenty-first century. Similar analysis with the method
applied here could provide information about the trend
of allergic pollen concentration over Central Europe.
5 Summary and conclusion
In this study, the influence of atmospheric circulation
conditions, as described by specific circulation types,
on Alnus and Betula pollen concentrations in Wro-
claw, Poland, was analysed for the period from 2005 to
Fig. 10 Number of days for
the NWAA type in March
(upper left), NWAA in May
(upper right), SWAA in May
(bottom left), and SWCC in
May (bottom right) for the
period 1948–2017. Trend
line is in red
123
Aerobiologia (2020) 36:261–276 273
2014. The results show that pollen concentrations vary
significantly according to circulation types. The main
findings of this work are the following:
1. The highest pollen concentrations for both Alnus
and Betula are observed for warm, sunny, and dry
anticyclonic circulation types with anticyclone in
the lower and upper troposphere, especially for
types with advection from SW. The lowest pollen
concentrations are observed for cold, wet, and
cloudy cyclonic types with advection from the
northern sectors.
2. Sunshine duration could additionally influence
pollen concentration (for both Alnus and Betula)
regardless of the conditions connected with
specific circulation types.
3. Apart from changes in the daily pollen concen-
tration, the influence of circulation types could be
noticeable in SPIn as well. There are some
significant correlations between the SPIn of both
Betula and Alnus and the frequency of specified
circulation types.
4. Positive and statistically significant trends in the
frequency of circulation types favourable for high
concentrations of Betula and Alnus were shown
for the last 70 years (1948–2017).
5. The method used here is flexible in terms of
application to other geographical areas and dif-
ferent gridded meteorological data.
Acknowledgements NCEP reanalysis data provided by the
NOAA/OAR/ESRL PSD, Boulder, Colorado, USA, from their
website at http://www.esrl.noaa.gov/psd/. This study was sup-
ported by the Polish National Science Centre (Project Nos.
UMO-2017/25/N/ST10/0049 and UMO-2017/25/B/ST10/
00926).
Open Access This article is licensed under a Creative Com-
mons Attribution 4.0 International License, which permits use,
sharing, adaptation, distribution and reproduction in any med-
ium or format, as long as you give appropriate credit to the
original author(s) and the source, provide a link to the Creative
Commons licence, and indicate if changes were made. The
images or other third party material in this article are included in
the article’s Creative Commons licence, unless indicated
otherwise in a credit line to the material. If material is not
included in the article’s Creative Commons licence and your
intended use is not permitted by statutory regulation or exceeds
the permitted use, you will need to obtain permission directly
from the copyright holder. To view a copy of this licence, visit
http://creativecommons.org/licenses/by/4.0/.
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